If your not on the pill its a wait and see time, unless this was within the last 72v hours, if so you could take Plan B, this will overcome your problem.
If not its a case of wait to see if you get your next period, the thing now is not to stress, or stress will stop your next period, putting even more stress on you.
Time to think of the BC pill, remember safe sex is the best sex..
Hope this helps you.
Good Luck Dr. Cody Johnson